Historically, positive displacement machines and turbomachines, such as blowers and compressors, have been used to generate compressed or pressurized gas. Turbomachines are high technology machines that typically involve high engineering, production and assembly costs in order to achieve and maintain desired levels of performance and efficiency with reduced repair and safety concerns. Such high costs are typically due to complex design issues, lengthy assembly procedures, and detailed maintenance requirements, all greatly influenced by the operational requirements for the machinery. For example, fuel cell systems used in diverse stationary, mobile, military and commercial applications use blowers and compressors to pressurize high temperature process gas, but require the machinery to fit a tight footprint so as to not take up too much space, without compromising operation and efficiency of the overall system. Additionally, suitable blowers and compressors have long been desired to achieve high reliability and maintain high efficiency at high operating temperatures. Because of the high temperatures exerted on and by any systems using such machines, adequate insulation, cooling, design and safety precautions are required. However, these concerns must be addressed without affecting the desired size of the blowers and compressors.
There exist several patents on high temperature blowers for various applications that range from heat treat furnace blowers to blowers for simple cooking ovens. One such blower, as described in U.S. Pat. No. 2,694,157, uses a fan-bladed impeller, ball bearings, an electric motor, and secondary air to operate in a heat treat furnace environment with elevated temperatures. This prior art design, while good for a simple bulky application, lacks sufficient design features required to operate in an environment where the process gases are volatile or hazardous to the environment. These machines are also often very large in size due to low operational rotating speeds, and as so sized, are usually insufficient for installation many high temperature applications. Moreover, such blowers are often too big for many modern applications and the size cannot be reduced without compromising operation, efficiency, and safety, especially when used in high temperature applications. The blower also has low efficiency and uses ball bearings that require regular service intervals and can also cause contamination to the process through leaking seals. The use of such motor-driven machines—where process gas has been transported by various designs using oil lubricated ball bearings—are typically unreliable at high temperatures (about 1600° F.) due to oil coking and oil migration, insufficient cooling capacity, contamination, and safety hazards.
Another patent, U.S. Pat. No. 5,375,651, describes a high temperature draft blower for use in furnace applications at temperatures of about 400-450° F. The blower design uses a squirrel cage style impeller mated to a conventional motor using a heat shield to protect the motor from the elevated temperatures in the blower housing. The blower has an estimated overall efficiency of only about 20%, and uses an electric motor that is exposed to the environment. Such a design is undesirable due to high susceptibility to contamination, especially to the motor, which effects overall operation and efficiency of the blower.
U.S. Pat. No. 6,951,241 discusses a method of cooling a high temperature furnace blower motor to keep the internal bearings cool during operation to increase the life of the blower. The method uses holes provided in the motor housing and at the impeller back plate to cool the blower. Specifically, the holes allow external air to be drawn into the blower housing and over the motor and then into the impeller portion of the blower housing. Hot air goes out through an exhaust port incorporated into the blower housing design. Due to limited cooling capacity from such a design, the blower is highly inefficient. Noise levels are also very high, even where a secondary cooling fan—typically used in such a design—is eliminated. Moreover, the ball bearings used inside the blower do not reduce noise levels to satisfactory levels. Additionally, since the holes in the blower housing are critical to drawing in external air to cool the motor and the impeller in such a design, the blower cannot be hermetically sealed. As a consequence, the process gas can easily mix with ambient air, which can be hazardous, especially at the high temperatures to which such a blower may be subjected.
In view of the foregoing, there is a need for a blower design that can operate efficiency at high temperatures, in a small, compact size, without suffering from the drawbacks common to prior art blower designs that tend to affect performance, operation and efficiency, and moreover, tend to compromise product safety. Accordingly, it is a general object of the present invention to provide a high temperature blower that overcomes the problems and drawbacks associated with the use of blowers at high temperatures (e.g., about 1600° F.).
The proposed high temperature centrifugal blower of the present invention avoids the drawbacks common to prior art blower designs, such as those discussed above, by using a unique internal cooling circuit that is self-sustaining. There is need for a blower design for use at high temperatures that is hermetically sealed and thus does not allow any leaking of the process gas. The present invention also uses foil gas bearing technology that permits a sealed, contamination fee, high speed, efficient, self-cooling centrifugal blower system. Such foil gas bearing technology also has no sliding contact of surfaces, and hence, improves the efficiency and reduces noise levels in the unit.